Recirculating furnace



Nov. 28, 1933.

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RECIRCULATING FURNACE Filed April 22, 1931 2 Sheets-Sheet 1 '0 6 /4/9455 5. ma /ya Nov. 28, 1933.

C. B, THORNE RECIRCULATING FURNACE Filed April 22. 1931 2 Sheets-Sheet 2 (HA/94:5 5 7205M: 3%

Patented Nov. 28, 1933 UNITED STATES PATENT oFrlcs 1,937,395 RECIRCULATING FURNACE Charles B. Thorne, Shaker Heights, Ohio Application April 22,-1931. Serial No. 532,004

' 13 Claims. (01. 263-6) This invention relates to heating furnaces and more particularly to apparatus for eliminating stratification and consequent cold spots in annealing furnaces.

In the manufacture of metal sheets, pipe and the like, it is commonly necessary to heat the articles at various stages of their manufacture.

This is frequently done by passing the articles continuously through a relatively long heating chamber, the material entering at one end, being heated as they pass through the chamber, and being discharged at the other end at the desired temperature. These furnaces may be of considerable length and for this reason trouble has been experienced in maintaining the desired tempera ture throughout all parts of the furnace. The

gases within the furnace tend to stratify and form nace; the provision of a furnace which may be accurately maintained at the desired uniform temperature; the provision of means for withdrawing a portion of the products of combustion from the flue of a furnace, re-heating them to the desired temperature and re-directing them into the furnace to cause an active circulation of gases within the furnace; the provision of a simple and economical re-heating and re-circulating apparatus for furnaces which is adapted to create a positive circulation of gases through the furnace without the use of fans, blowers or the like.

.The above and other objects of my invention will appear from the following description of one form thereof, reference being had to the accompanying drawings in which- Fig. 1 is a longitudinal section through a heating furnace designed for heating pipe and incorporating my recirculating features.

Fig. 2 is a fragmentary end view taken on line 2-2 of Fig. 1.

Fig. 3 is a horizontal section illustrating the re-circulating apparatus and. taken on line 3--3 of Fig. 1.

In the furnace illustrated in the drawings the fuel enters the combustion chamber 1 through a plurality of burners 2 which are suitably disposed along the upper portion of the walls 3 and. 4 of the furnace. In the preferred operationof this type of furnace a mixture of oil or gas and air in the proper proportions is admitted through the burners 2 and'complete combustion takes place within the portion of the furnace generally indicated at 1." The hot burned gases then pass through the heatingchamberor portion of the furnace indicated at-5, which is of reduced cross section. and then out'through the downwardly extending flue 6, the connecting flue 7, and "are discharged to the atmosphere through the vertical flue or chimney 8.

I'have illustrated the furnace as equipped for the heating of pipes 9. These pipes 9 may enter the furnace on a roller conveyor 10 and are then traversed through the'furnace by means of any suitable means, such as the walking beam conveyor 11.

when they reach the trough 12 they have attained the desired temperature. Apparatus of well known type (not shown) may be used'to withdrawthe pipe longitudinally from the trough 12 of the furnace.

In furnaces of this type re -circulating apparatus considerable difficulty is experienced. because of the stratification of the.

burned products of combustion in the area 5 of .the furnace. This Stratification frequently results in the formation of hot and cold zones which make it very difficult to secure the desired heating results.

Toovercome Iprovide ducts 13 and14 connected to and extending outwardly from opposite sides of the chimney 8. As best'seen in Fig. 3'

theseducts 13 and 14 connect at their outer ends to ducts 15and 16 through Venturi shaped passages 1'? and 18-respectively. Enlarged cylindrical auxiliary combustion chambers 19 and 20 are disposed atthe-ends-of the ducts 15 and 1e and are arranged co-axially" therewith. 7 These auxiliary combustion chambers communicate with the ducts 15 and 16 through the pipes 21 and 22. Thesepipes 21and 22 form passages leading from' the interior of the auxiliary combustion chambers and terminatingapproximately at the narrowest point of the Venturi sections 17 and 18. Burners 23 and 24 are located in the rear The furnace is so operated that the pipes move continuously through the furnace and notequipped with my walls of the auxiliary'combustion chambers and.

may be adapted to burn oil, gas or other suitable fuel. V V

Damper valves 25 and 26 are disposed in the ducts 13 and 14 and serve to assist in the regulation of the quantity of flue gas which is with drawn from the chimney 8 and recirculated through the furnace. The ducts 15 and 16 may be connected to transverse conduits 27 and 28. The gas from these conduits is led back into the furnace through suitable elongated Openings 29 which extend substantially the full width of the furnace and evenly distribute the re-heated products of combustion.

The operation of the furnace is as follows:

Assuming that the fuel furnished through the burners 2 has been completely burned in the combustion area 1 of the furnace the products of combustion pass out of the furnace through the conduits 6, 7 and the chimney 8. The auxiliary burners 23 and 24 inject fuel into the auxiliary combustion chambers 19 and 20. These chambers are so proportioned and the burners are so adjusted that complete combustion of the fuel entering through burners 23 and 24 takes place within the auxiliary chambers 19 and 29. The hot burned products of combustion are then expelled through the pipes 21 and 22 with considerable force and, as they pass into the ducts 15 and 16 through the Venturi sections 17 and 18, an injector action is created which draws a certain portion of the burned gases which are'passing out through the chimney 8 back into the conduits 15 and 16.

As the burned gas which emerges from the pipes 21 and 22 is at relatively high temperature it will add heat to the flue gases which are drawn into the ducts 17 and 18 by the injector effect and the gases which are forced back into the furnace through. the openings 29 will be re-heated to the proper temperature.

For example, if the temperature within the furnace immediately below the openings 29 is 1700 and the temperature at the outlets 6 where the gases leave the furnaceis 1590" it is evident that the gas which re-enters the furnace through the openings 29 should be heated to at least 1700". To accomplish this'the dampers 25 and 26 are so adjusted and the burners 23 and 24 so set that sufficient heat will be added to the gas withdrawn from the chimney 8 to bring it back up to 1700".

Thus by properly co-ordinating the combustion within the auxiliary chambers 19 and 20 with the setting of the dampers 25 and 26 inert burned gas at the desired temperature may be forced back into the furnace through the openings 29. By completely burning the fuel from the burners 23 and 24 before it passes out of the auxiliary combustion chambers 19 and 20 and before it enters the furnace through the openings 29, I eliminate all danger of adding unburned gas to the zone 5 of the furnace. It is desired to maintain this heating chamber or portion 5 of the furnace filled with inert non-oxidizing gas to eliminate as far as' possible oxidization of the material passing through the furnace.

It will be seen by those skilled in the art that I have provided a furnace in which the products of combustion may be re-circulated and the temperature of the products of combustion which are recirculated may be easily and accurately controlled. The re-circulating draft is created by the pressure of the mixture of fuel and air which enters the auxiliary combustion chambers 23 and 24 and it is unnecessary to use any blowers or fans. Such blowers or fans are objectionable because of difficulties which are encountered in operating this type of apparatus at high temperature.

My furnace has no moving parts other than the dampers and is susceptible to very accurate and convenient regulation. Although I have illustrated and described herein a preferred embodiment of my invention, it will be seen by those skilled in the art that modifications and variations thereof may be made without departing from the spirit of my invention. I do not, therefore, limit myself to the specific form shown and described but claim as my invention all embodiments thereof coming within the scope of the appended claims.

I claim:

1. In combination with a heating furnace having a combustion chamber, a heating chamber and a chimney, an auxiliary combustion chamher, a recirculatin duct leading from the chimney back into said heating chamber and having a Venturi section, and means for discharging products of combustion from said auxiliary combustion chamber into the throat of said Venturi section to create a recirculating flow of gas from said chimney back into the heating chamber of the furnace.

2. In combination, a furnace having a heating chamber, a duct for conducting away the products of combustion from said heating chamber, an auxiliary combustion chamber, a recirculating duct leading from said first named duct back to said heating chamber, and means for directing the products of combustion from said auxiliary combustion chamber into said recirculating duct in a direction to create a flow of gas through sai recirculating duct into said heating chamher.

3. A furnace having a main combustion chamber and a heating chamber, a recirculating duct extending from a point adjacent one end of said heat chamber and re-entering said heating chamer at a pointremoved from said end of the heating chamber, an auxiliary combustion chamber disposed at a point removed from said main combustion chamber and means for discharging the products of combustion from said auxiliary combustion chamber into said recirculating duct whereby gas from said heating chamber will be drawn from the end of said chamber, reheated, and injected back into said heating chamber together with the products of combustion from said auxiliary combustion chamber.

4. In combination with a furnace having a heating chamber disposed out of the zone of combustion of the furnace and a recirculating gas passage adapted to take gas from one part of said chamber and re-direct it back into another part of said chamber, an auxiliary combustion chamber, means for injecting a combustible mixture into said auxiliary combustion chamber and means for directing the products of combustion of said mixture into said recirculatpassage.

5. In' combination in a furnace of the type described having a combustion chamber and a heating chamber, a recirculating gas passage adapted to take gas from one part of said heating chamber and re-direct it back into another part of said heating chamber, a damper valve in said passage, an auxiliary combustion chamber, means for injecting a combustible mixture into said auxiliary combustion chamber and means for directing the products of combustion of said mixture into said recirculating passage.

6. In combination in a furnace of the type described having a combustion chamber and a heating chamber, a recirculating gas passage having a Venturi section, an auxiliary combustion chamber and a pipe extending from said auxiliary combustion chamber into the throat of said Venturi section of said recirculating passage.

7. In a furnace of the type described a combustion chamber, an elongated heating chamber extending from said combustion chamber, a flue leading from said heating chamber at a point removed from said combustion chamber and adapted to conduct the products of combustion from said heating chamber to a place of discharge, a recirculating duct leading from said flue and entering said heating chamber, said duct having a Venturi shaped portion, a valve in said duct adapted to control the flow of gas therethrough and being disposed between said heating chamber and said Venturi portion of said duct, an auxiliary combustion chamber, means for in-' jecting a combustible mixture into said auxiliary combustion chamber under pressure and a pipe extending from said auxiliary combustion chamber and discharging into said duct substantially at the, throat of said Venturi portion whereby a recirculating flow of gas from said heating chamber, through said duct, and'back into said heating chamber will be created.

8. In combination in a heating furnace having a main combustion chamber and a heating chamber, a flue for carrying away products of combustion therefrom, a recirculating duct leading from said' flue into said heating chamber and means, independent of said main combustion chamber, for increasing the temperature of gas flowing through said recirculating duct.

9. In combination in a heating furnace having a main combustion chamber and a heating chamber, a flue for carrying awayproclucts of combustion therefrom, a recirculating duct leading from said flue into said heating chamber, and means, independent of said main combustion chamber, for inducing a flow of gas from said flue through said recirculating. duct and increas ing the temperature of said gas before it reenters the furnace.

10. In combination in aheating furnace having: a main combustion chamber and a heating chamber, a flue for carrying away products of combustion therefrom, a recirculating duct leading from said flue into said heating chamber, a damper: valve in said duct, and means, independent of said main combustion chamber, for increasing the temperature of gas flowing through said recirculating duct.

11. In combination in a heatingfurnace having a main combustion chamber and a heating chamber, a flue for carrying away products of combustion therefrom, a recirculating duct leading from said flue into said heating chamber, a damper valve in said duct, and means, independent of said main combustion chamber, for inducing'a flow of gas from said flue through said recirculatingduct and increasing the temperature of said gas before it reenters the furnace.

12. In combination in a heating furnace having a main combustion chamber, a heating chamber in communication therewith and a gas conducting passage for carrying away products of combustion from said heating chamber, a recirculating duct leading from said passage back into said heating chamber, means, independent of said main combustion chamber, for increasing the temperature of gas flowing through said recirculating duct and means for controlling the flow of gas from said passage through said duct.

13. In combination in a furnace having a main combustion chamber and a heating chamber in communication therewith, a flue for carrying away products of combustion from said heating chamber, a recirculating duct leading from said 110 flue to said heating chamber, a damper valve in said duct, an auxiliary combustion chamber, and means for injecting heatedgas from said auxiliary combustion chamber into said duct at a point between said damper valve and said heating 115 chamber.

CHARLES B. THORNE. 

